att: support for delayed att read response

src/ble/att_db.c

@@ -494,6 +494,10 @@ static uint16_t handle_read_by_type_request2(att_connection_t * att_connection,
     uint8_t error_code = 0;
     uint16_t first_matching_but_unreadable_handle = 0;
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    int read_request_pending = 0;
+#endif
+
     while (att_iterator_has_next(&it)){
         att_iterator_fetch_next(&it);
         
@@ -520,6 +524,13 @@ static uint16_t handle_read_by_type_request2(att_connection_t * att_connection,
 
         att_update_value_len(&it, att_connection->con_handle);
         
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+        if (it.value_len == ATT_READ_RESPONSE_PENDING){
+            read_request_pending = 1;
+        }
+        if (read_request_pending) continue;
+#endif
+
         // check if value has same len as last one
         uint16_t this_pair_len = 2 + it.value_len;
         if (offset > 1){
@@ -549,6 +560,10 @@ static uint16_t handle_read_by_type_request2(att_connection_t * att_connection,
         offset += bytes_copied;
     }
     
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    if (read_request_pending) return ATT_READ_RESPONSE_PENDING;
+#endif
+
     // at least one attribute could be read
     if (offset > 1){
         response_buffer[0] = ATT_READ_BY_TYPE_RESPONSE;
@@ -609,6 +624,10 @@ static uint16_t handle_read_request2(att_connection_t * att_connection, uint8_t
 
     att_update_value_len(&it, att_connection->con_handle);
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    if (it.value_len == ATT_READ_RESPONSE_PENDING) return ATT_READ_RESPONSE_PENDING;
+#endif
+
     uint16_t offset   = 1;
     // limit data
     if (offset + it.value_len > response_buffer_size) {
@@ -657,6 +676,10 @@ static uint16_t handle_read_blob_request2(att_connection_t * att_connection, uin
 
     att_update_value_len(&it, att_connection->con_handle);
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    if (it.value_len == ATT_READ_RESPONSE_PENDING) return ATT_READ_RESPONSE_PENDING;
+#endif
+
     if (value_offset > it.value_len){
         return setup_error_invalid_offset(response_buffer, request_type, handle);
     }
@@ -698,6 +721,11 @@ static uint16_t handle_read_multiple_request2(att_connection_t * att_connection,
     int i;
     uint8_t error_code = 0;
     uint16_t handle = 0;
+
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    int read_request_pending = 0;
+#endif
+
     for (i=0;i<num_handles;i++){
         handle = little_endian_read_16(handles, i << 1);
         
@@ -725,6 +753,13 @@ static uint16_t handle_read_multiple_request2(att_connection_t * att_connection,
         }
         att_update_value_len(&it, att_connection->con_handle);
         
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+        if (it.value_len == ATT_READ_RESPONSE_PENDING) {
+            read_request_pending = 1;
+        }
+        if (read_request_pending) continue;
+#endif
+
         // limit data
         if (offset + it.value_len > response_buffer_size) {
             it.value_len = response_buffer_size - 1;

src/ble/att_db.h

@@ -48,12 +48,15 @@ extern "C" {
 #endif
 
 // custom BTstack error codes
-#define ATT_ERROR_HCI_DISCONNECT_RECEIVED          0x1f
+#define ATT_ERROR_HCI_DISCONNECT_RECEIVED         0x1f
 
 // custom BTstack ATT error codes
-#define ATT_ERROR_DATA_MISMATCH                    0x7e
+#define ATT_ERROR_DATA_MISMATCH                   0x7e
-#define ATT_ERROR_TIMEOUT                          0x7F
+#define ATT_ERROR_TIMEOUT                         0x7F
-    
+
+// custom BTstack ATT Response Pending 
+#define ATT_READ_RESPONSE_PENDING                 0xffff
+
 typedef struct att_connection {
     hci_con_handle_t con_handle;
     uint16_t mtu;       // initialized to ATT_DEFAULT_MTU (23), negotiated during MTU exchange
@@ -66,6 +69,7 @@ typedef struct att_connection {
 // ATT Client Read Callback for Dynamic Data
 // - if buffer == NULL, don't copy data, just return size of value
 // - if buffer != NULL, copy data and return number bytes copied
+// If ENABLE_ATT_DELAYED_READ_RESPONSE is defined, you may return ATT_READ_RESPONSE_PENDING if data isn't available yet
 // @param con_handle of hci le connection
 // @param attribute_handle to be read
 // @param offset defines start of attribute value
@@ -130,7 +134,8 @@ void att_dump_attributes(void);
  * @param att_connection used for mtu and security properties
  * @param request_buffer, request_len: ATT request from clinet
  * @param response_buffer for result
- * @returns len of data in response buffer. 0 = no response
+ * @returns len of data in response buffer. 0 = no response, 
+ *          ATT_READ_RESPONSE_PENDING if it was returned at least once for dynamic data (requires ENABLE_ATT_DELAYED_READ_RESPONSE)
  */
 uint16_t att_handle_request(att_connection_t * att_connection,
                             uint8_t * request_buffer,

src/ble/att_server.c

@@ -340,6 +340,16 @@ static int att_server_process_validated_request(att_server_t * att_server){
     uint8_t * att_response_buffer = l2cap_get_outgoing_buffer();
     uint16_t  att_response_size   = att_handle_request(&att_server->connection, att_server->request_buffer, att_server->request_size, att_response_buffer);
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+    if (att_response_size == ATT_READ_RESPONSE_PENDING){
+        // update state
+        att_server->state = ATT_SERVER_READ_RESPONSE_PENDING;
+
+        // callback with handle ATT_READ_RESPONSE_PENDING
+        att_server_client_read_callback(att_server->connection.con_handle, ATT_READ_RESPONSE_PENDING, 0, NULL, 0);
+    }
+#endif
+
     // intercept "insufficient authorization" for authenticated connections to allow for user authorization
     if ((att_response_size     >= 4)
     && (att_response_buffer[0] == ATT_ERROR_RESPONSE)
@@ -374,6 +384,18 @@ static int att_server_process_validated_request(att_server_t * att_server){
     return 1;
 }
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+int att_server_read_response_ready(hci_con_handle_t con_handle){
+    att_server_t * att_server = att_server_for_handle(con_handle);
+    if (!att_server)                                             return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
+    if (att_server->state != ATT_SERVER_READ_RESPONSE_PENDING)   return ERROR_CODE_COMMAND_DISALLOWED;
+
+    att_server->state = ATT_SERVER_REQUEST_RECEIVED_AND_VALIDATED;
+    att_dispatch_server_request_can_send_now_event(con_handle);
+    return ERROR_CODE_SUCCESS;
+}
+#endif
+
 static void att_run_for_context(att_server_t * att_server){
     switch (att_server->state){
         case ATT_SERVER_REQUEST_RECEIVED:
@@ -829,7 +851,6 @@ void att_server_register_can_send_now_callback(btstack_context_callback_registra
     att_dispatch_server_request_can_send_now_event(con_handle);
 }
 
-
 int att_server_notify(hci_con_handle_t con_handle, uint16_t attribute_handle, uint8_t *value, uint16_t value_len){
     att_server_t * att_server = att_server_for_handle(con_handle);
     if (!att_server) return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;

src/ble/att_server.h

@@ -112,6 +112,16 @@ int att_server_notify(hci_con_handle_t con_handle, uint16_t attribute_handle, ui
  */
 int att_server_indicate(hci_con_handle_t con_handle, uint16_t attribute_handle, uint8_t *value, uint16_t value_len);
 
+#ifdef ENABLE_ATT_DELAYED_READ_RESPONSE
+/*
+ * @brief read response ready - called after returning ATT_READ_RESPONSE_PENDING in an att_read_callback before
+ * @nore The ATT Server will retry handling the current ATT request
+ * @param con_handle
+ * @return 0 if ok, error otherwise
+ */
+int att_server_read_response_ready(hci_con_handle_t con_handle);
+#endif
+
 /* API_END */
 
 #if defined __cplusplus